The present invention relates to a punch rivet for connecting two workpieces, with a head and a shank, the shank being embodied as a hollow shank having a shank internal diameter, a shank external diameter and a shank end face, there being embodied at the shank end face an annular cutting edge, the diameter of which is smaller than the shank external diameter, and the shank internal diameter merging with the annular cutting edge via a cutting edge radius.
A punch rivet of this type is known from document DE 10 2005 052 360 B4.
The invention further relates to a method for producing a punch rivet connection of at least two workpieces, of which one is made, in particular, of a high-strength material having a strength of at least 800 MPa and has, in particular, a thickness of at least 0.5 mm. The present invention further relates to a workpiece arrangement made up of at least two workpieces which are connected by means of at least one punch rivet of this type or by means of a punch riveting method of this type.
Punch riveting is a reshaping joining method and can be carried out by means of what are known as solid rivets and what are known as semitubular rivets. The present case relates to punch riveting with a semitubular rivet which is embodied with a hollow shank. This method is characterized in that the semitubular rivet is driven into an arrangement of two workpieces (in particular two metal sheets), the top workpiece being punched through (pierced) by the hollow shank. A die plate on which the bottom workpiece rests is designed in such a way that the hollow shank is subsequently radially spread and is driven radially into the lower workpiece, thus forming an undercut. In this case, the lower workpiece is generally not severed, so that the side of the lower workpiece that faces the die plate remains closed and accordingly has low susceptibility to rusting. This punch riveting method with a semitubular rivet has for years increasingly been used in the automotive industry. The punch riveting method is suitable, in particular, for connecting workpieces made of different material (for example steel and aluminium). As, in particular in body construction, there is a trend toward a combination of different materials adapted to the respective purpose of application, the punch riveting method is for this case a joining method which is preferable over welding methods.
It will in this case be understood that at least the material of the lower, die plate-side workpiece should be readily cold formable and have material properties which are as homogeneous as possible.
As, in the above-described field of application, there is a trend toward high-strength materials (for example materials of the upper, swage-side workpiece of greater than 1,000 MPa), the punch rivets used for this purpose have to have a correspondingly higher strength (rivet hardness), in particular in order to be able to punch through a workpiece of this type made of a high-strength material. At the same time, the punch rivet should be sufficiently deformable in its shank region to ensure a sufficient undercut in the finished punch rivet connection.
In the field of semitubular rivets there are various types, for example what is known as the C rivet such as is known from document WO 95/09307. The semitubular rivet described therein has a cylindrical hollow shank, a sharp annular cutting edge being formed at the outer edge of the end face of the shank. For this purpose, the internal diameter merges with the shank external diameter via a cutting edge radius. However, this C rivet is less suitable for the punch riveting of high-strength materials, as the C rivet has a tendency to spread intensively during the punch riveting process, so that only little material is present in the undercut region of the lower workpiece. The strength which may be achieved is accordingly relatively low. A modified C rivet with a sharp annular cutting edge, which is however set apart from the shank external diameter, is known from document DE 203 19 610 U1.
Furthermore, what is known as a P rivet is known in the art, for example from document DE 10 2005 052 360 B4.
In this punch rivet there is formed at the shank end face an annular cutting edge, the diameter of which is smaller than the shank external diameter. The annular cutting edge is embodied as a planar annular surface which is oriented in the radial direction, merges with the shank external diameter via a shank outer chamfer and is thus set apart from the shank external diameter. The shank internal diameter merges with this annular surface via a relatively small radius.
Although the P rivet has better properties than the C rivet in the punch riveting of high-strength materials, there is nevertheless still a need for improvement even over the P rivet in this regard.